It's estimated that anywhere from three to seven percent of school-age children may have dyslexia, a neurodevelopmental issue that affects reading, spelling, and writing. There are different ideas about why dyslexia occurs, although they relate to dysfunction in brain networks, and are likely due to multiple causes in affected individuals; the disorder may not have a singular underlying cause. Neuroimaging studies of dyslexic individuals have produced inconsistent results.
Since dyslexia has a heritable, and therefore, genetic component, scientists wanted to know more about how genetics and brain mapping could reveal more about the pathology of dyslexia. A new study has shown that carriers of genetic variants that increase the risk of dyslexia also have changes in brain structure, which occur in areas that are related to language, motor coordination, and vision. The findings have been reported in Science Advances.
Although dyslexia has a genetic component, it is complex, and is not due to changes in one gene or brain region, noted first study author Sourena Soheili-Nezhad, of the Max Planck Institute for Psycholinguistics in Nijmegen. "Studying exactly which genes affect which brain networks can help to understand how cognitive functions develop differently in this learning difficulty."
In this study, the researchers utilized data from over one million people, which was collected by the genetics company 23andMe, and more than 30,000 adults who participated in the UK Biobank.
The UK Biobank information was also used to calculate scores that assess a person's risk of developing dyslexia, which was linked to brain scans. While the UK Biobank does not keep track of dyslexia, all of this data together could be used to find genetic variants linked to dyslexia (from 23andMe), and to then identify changes in the brain scans (in the UK Biobank) that were associated with the dyslexia risk variants.
The investigators showed that individuals who had a higher genetic risk of dyslexia also had lower brain volumes in areas that are related to speech sound processing and movement coordination; these variants were also associated with higher volumes in the brain's visual cortex.
The study also indicated that dyslexic individuals have changes in a brain region known as the internal capsule, which is a bundle of white matter. White matter density in this region was also linked to educational attainment, attention deficit/hyperactivity disorder (ADHD), and fluid intelligence.
The findings seem to confirm that dyslexia is complex and related to changes in multiple cognitive processes, noted senior study author Professor Clyde Francks, a Senior Investigator at the Max Plack Institute, among other appointments.
The team is interested in analyzing data from dyslexic adolescents in future work instead of focusing on adults as this study did, so they may be able to gain more insights into the causes of dyslexia.
"Understanding the brain basis of dyslexia could also possibly help to achieve earlier diagnosis and educational intervention in the future, with more targeted strategies suited to the profiles of individual children," added Soheili-Nezhad.
Sources: Max Planck Society, Science Advances
